3-coil wireless power transfer system for eye implants

ABSTRACT

A three-coil electromagnetic induction power transfer system is disclosed for epiretinal prostheses and other implants. A third, buffer coil is disposed between an external transmitting coil and a receiver coil buried within the body to improve efficiency and robustness to misalignments. One or more of the coils can be manufactured using micromechanical machining techniques to lay out conductors in a ribbon of biocompatible insulator, folding lengths of the insulated conductor traces longitudinally over one another, and then spiraling them into a ring. The traces change axial position in the ring by shifting across fold lines. One or more U-shaped sections on the traces can be folded so that adjacent traces can project opposite one another, lengthening the resulting ribbon that can be wound into a coil.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/692,138, filed Aug. 22, 2012, which is hereby incorporated byreference in its entirety for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

This invention was made with government support under EEC0310723 awardedby the National Science Foundation. The government has certain rights inthe invention.

BACKGROUND

1. Field of the Art

Embodiments of the present invention generally relate to wireless powertransfer to surgically implanted prostheses, in particular, to athree-coil power transfer system with one of the coils being a fullyintraocular coil.

2. Description of the Related Art

Age-related macular degeneration (AMD) and retinitis pigmentosa (RP) aretwo most common outer-retina degenerative diseases of the human eye.There is promise in the use of retinal prostheses in order to allowpeople afflicted with the diseases to see. Retinal prostheses, whichbypass the defective outer-retina photoreceptors and electricallystimulate the inner-retina neurons directly, have allowed some blindpeople with AMD and RP to perceive light.

It is recognized that these early prostheses only involve a very smallnumber of stimulating electrodes on the neurons. To realize facialrecognition or large-sized letter reading, next-generation retinalprosthetic devices may use 1024 or more stimulating electrodes.

Unfortunately, the high-resolution sensors and processors haverelatively high power consumption, for example, greater than 100milliwatts (mW). Current battery technology limits their usefulness forsuch implants, so power is preferably drawn from outside the body.Cables tend to be unwieldy for connecting a patient's eye to an externalpower source, so wireless power transfer is preferred.

Electromagnetic inductive coupling between two coils has been widelystudied and optimized for wirelessly powering retinal prostheticdevices. However, because of the extremely demanding physicalconstraints in and around the eye, the physical placement of theimplanted receiver coil remains a matter of ongoing debate. There aretradeoffs between the power-transfer capability, surgical risk andlong-term implantation. While there are fewer constraints on atransmitting coil, which is outside the body, it cannot be too powerfullest it heat the receiver coil too much or subject the patient tounacceptable levels of electromagnetic fields.

Generally, the inductive link efficiency between two coils isproportional to the square of the coupling coefficient (k) and therespective quality factors (Qs) of coupled coils. Wireless powertransfer naturally involves no magnetic transformer core around which aprimary winding and a secondary winding are wound as in a conventionalelectrical transformer. Instead, wireless inductively-linked coils arecoupled through the air (or other intervening media).

In the prior art, to compensate for the low-efficiency of this air-coredcoupling and satisfy safety limitations, such as heat dissipation,electromagnetic field exposure, etc., the receiver coils are placedextraocular and connected to the electrodes sitting intraocular througha cable that penetrates the eyeball. To penetrate the eyeball into theinside, one typically penetrates the eye's sclera and choroid. Thistrans-sclera, trans-choroid cable potentially causes infection andhypotony in the long-term implantation.

Fully-intraocular retinal implants have been attempted that place thereceiver coil inside the lens capsule after removing the natural lens.However, with a 25 millimeter (mm) (1-inch) separation between thetransmitter and receiver coils, this 2-coil configuration suffers lowefficiency (e.g., 7%) from the limited Q of the receiver coil and thesmall coupling coefficient k between the coupled coils.

There exists a need in the art for more efficient wireless electricalpower transfer methods for retinal implants.

BRIEF SUMMARY

Generally, a third coil, called a “buffer coil,” is introduced betweenthe transmitter coil and receiver coil to increase power transferefficiency between the transmitter coil and receiver coil. In particularwith the physical constraints of the human eye, an intervening buffercoil fits into the available spaces well. In some instances, it may notneed to be surgically implanted at all, but instead worn by a patient asa sclera lens.

The buffer coil and/or receiver coil can be geometrically oblong, suchas an oval, in order to account for greater movement of the eye in thehorizontal direction as opposed to the vertical direction.

A high-Q receiver coil of the size that can fit in tight places withinthe human body can be manufactured using both micromachining—andorigami—techniques. Thin, conductive traces are laid out on a flatsubstrate within a flexible insulator and then peeled from thesubstrate. Swaths of traces in the flexible insulator are then foldedover one another. The resulting folded traces are coiled into a ring.The ring, or coil, can be pinched radially so that it can be insertedthrough small incisions, and once released will snap back to its ringshape.

Electrical resistance caused by the skin effect can be minimized bysizing the electrical traces appropriately for the electromagneticinduction frequency. Further, the traces can be layed out so when theyare wound into the coil, the traces shift their axial positions so as toshare the (axial) outside positions, thus minimizing resistance causedby the proximity effect. The traces can shift axial positions by havingan outermost trace pass over a fold line (i.e., a crease) while an innertrace takes its place at the outermost position.

Because silicon wafer substrates can be small, a U-shaped section oftraces can effectively double the length of the traces to be coiled intoa coil. Multiple U-shaped sections can triple, quadruple, etc. thelength of the traces. Folding the U-shaped region up and then foldingthe two sides of the U together results in the traces that were onceadjacent on the substrate being disposed in opposite directions from oneanother.

The receiver coil can be fitted with an air-filled chamber, acting as afloatation device, and therefore meet effective mass constraints withinthey eye. The chamber can be filled with gas by a surgeon and oropportunistically capture air bubbles.

Although many of the embodiments discussed refer to the human eye,devices and methods for implanting into other portions of the body andother animal species are envisioned. Anywhere that wireless electricalpower transfer must be efficient may find use from aspects taughtherein.

Some embodiments of the present invention relate to aninductively-powered eye implant apparatus. The apparatus includes abuffer coil adapted to be affixed external to a sclera of an eye, thebuffer coil having a conductor covered by a biocompatible layer, areceiver coil adapted for implantation within the eye, the receiver coilhaving a conductor covered by a biocompatible layer, the receiver coiladapted for receiving electrical power by electromagnetic inductionthrough the buffer coil from a transmitter coil, the buffer coil andreceiving coil adapted to be electromagnetically coupled when affixedexternal to and implanted within the eye, respectively, and a processingcircuit connected with the conductor of the receiver coil and configuredto receive electrical power from the receiver coil.

The apparatus can include an array of stimulating electrodes adapted tobe connected with inner retina neurons in the eye and connected with theprocessing circuit, and an electrical cable coupling the receiver coilwith the array. The buffer coil can be suitable for mounting around thecornea and under the conjunctiva of the eye, or there can be a scleralens encasing the buffer coil, the sclera lens adapted to be worn on thesclera to thereby affix the buffer coil external to the sclera of theeye.

In some embodiments, the buffer coil is adapted to be affixed to a sideof the eye external to the sclera, and the receiver coil is adapted formounting within a vitreous body of the eye inside the sclera to aninternal side of the eye.

The apparatus can have a buffer coil that is circular and have an outerdiameter equal to or between about 19 millimeters and 20 millimeters. Orthe buffer coil can be oval and have an outer minor axis of about 19millimeters and an outer major axis of about 24 millimeters, the buffercoil adapted to be affixed external to the sclera such that the outermajor axis is substantially horizontal. The apparatus can have a buffercoil or receiver coil that is in a polygon shape as viewed from an axialdirection.

Optionally, the receiver coil of the apparatus is produced by etchingconductor traces on an electrically insulative sheet, depositingelectrical insulator over the etched conductor traces sufficient toembed the etched conductor traces in a biocompatible layer, folding thesheet over onto itself, stacking the embedded conductor traces, and thenwinding the folded sheet in a spiral to form a closed shape. Further,the conductor traces on the electrically insulative sheet can include aU-shaped region connecting two lengths of conductor traces that projectin a same direction from the U-shaped region. The production of thereceiver coil can further be produced by folding the sheet, before thewinding, such that the U-shaped region is perpendicular to the sheet,and then folding the U-shaped region such that the lengths of conductortraces project in opposite directions from the U-shaped region.

Some embodiments relate to a method of efficiently receiving powerinside an eye for an intraocular electronic device without ansclera-piercing cable. The method includes receiving, into a buffer coilaffixed external to a sclera of an eye, a varying magnetic field by wayof a first electromagnetic induction, the varying magnetic field causingcurrent in the buffer coil, inducing current, within a receiver coilwithin the eye, by way of a second electromagnetic induction from thecurrent in the buffer coil to the receiver coil, and powering anintraocular electronic device using the induced current from thereceiver coil.

The method can further include rectifying the induced current from thereceiver coil to generate direct current.

Some embodiments relate to a method of manufacturing a coil suitable forelectromagnetic induction. The method can include etching conductortraces on a substrate, the conductor traces underlaid by a sheet offlexible, biocompatible electrical insulator, depositing more electricalinsulator over the conductor traces to embed the conductor traces in theelectrical insulator, peeling the insulator embedded conductor tracesfrom the substrate to release a flexible ribbon of the embeddedconductor traces, folding the ribbon along one or more longitudinalcreases to stack the embedded conductor traces, and winding the ribbonin a spiral to form a closed shape, thereby forming a coil of stackedconductor traces.

The method can further include radially pinching the coil, and passingthe pinched coil through an incision in an eye. It can also includeconnecting pads or leads of the conductor traces to a processingcircuit, connecting the processing circuit to an array of stimulatingelectrodes adapted to be connected with inner-retina neurons in an eye,and coupling an electrical cable between the coil and the array.

The method can include sealing air within a chamber, and rigidlyattaching the chamber to the coil, thereby adding buoyancy to the coil.

The conductor traces on the sheet can include a U-shaped region, and themethod can include connecting two lengths of conductor traces thatproject in a same direction from the U-shaped region. The method canfurther include folding the ribbon, before the winding, such that theU-shaped region is perpendicular to the rest of the ribbon, and thenfolding the U-shaped region such that the lengths of conductor tracesproject in opposite directions from the U-shaped region.

Some embodiments relate to an inductively-powered implant apparatus. Theapparatus includes a buffer coil adapted to be affixed within a portionof a body of a patient, the buffer coil having a conductor covered by abiocompatible layer, a receiver coil adapted for implantation within adeeper portion of the body than the buffer coil, the receiver coilhaving a conductor covered by a biocompatible layer, the receiver coiladapted for receiving electrical power by electromagnetic inductionthrough the buffer coil from a transmitter coil, the buffer coil andreceiving coil adapted to be electromagnetically coupled, and aprocessing circuit connected with the conductor of the receiver coil andconfigured to receive electrical power from the receiver coil.

The portion of the body can includes a head and/or skull, and theprocessing circuit can include a brain pacemaker. The apparatus caninclude a torso, and the processing circuit can includes a spinal cordstimulator. The apparatus can include a rechargeable battery configuredto receive electrical power through and be recharged by the processingcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective illustration of an eyeball with aninductively-powered eye implant apparatus having a lens-mounted receivercoil in accordance with an embodiment.

FIG. 1B is a vertical cross section of the apparatus of FIG. 1A in vivoin which the buffer coil is mounted around the cornea and under theconjunctiva of the eye.

FIG. 1C is a vertical cross section of the apparatus of FIG. 1A in vivoin which the buffer coil is worn in a sclera lens.

FIG. 1D is a vertical cross section of the apparatus of FIG. 1A withoutthe eye shown for clarity of the dimensions.

FIG. 2 illustrates a wearable transmitter assembly with the transmittercoil in front in accordance with an embodiment.

FIG. 3 illustrates a wearable transmitter assembly with the transmittercoil on the side in accordance with an embodiment.

FIG. 4A is a picture of pinching and inserting into a lens capsule areceiver coil in accordance with an embodiment.

FIG. 4B is an annotated picture of the receiver coil of FIG. 4Aspringing to full diameter within the lens capsule.

FIG. 4C is a picture of the lens capsule of FIG. 4B with the eye's irisremoved for clarity.

FIG. 5 illustrates a receiver coil in accordance with an embodiment.

FIG. 6 illustrates a receiver coil held by tweezers in accordance withan embodiment.

FIG. 7 illustrates a ribbon of etched traces on a flat surface inaccordance with an embodiment.

FIG. 8 illustrates cross section 8-8 of FIG. 7.

FIG. 9 illustrates cross section 9-9 of FIG. 7.

FIG. 10 illustrates cross section 10-10 of FIG. 7.

FIG. 11 illustrates cross section 11-11 of FIG. 7.

FIG. 12 illustrates folding a ribbon of etched traces in accordance withan embodiment.

FIG. 13 illustrates further folding a ribbon of etched traces inaccordance with an embodiment.

FIG. 14 illustrates a fully (longitudinally) folded ribbon of stackedetched traces in accordance with an embodiment.

FIG. 15 illustrates a wound coil of etched traces in accordance with anembodiment.

FIG. 16 is a cross section of a wound coil of stacked etched traces,along with additional stacks of traces from a U-turn, in accordance withan embodiment.

FIG. 17 illustrates a flat sheet on a substrate in accordance with anembodiment.

FIG. 18 is cross section 18-18 of FIG. 17.

FIG. 19 illustrates etched conductor traces in accordance with anembodiment.

FIG. 20 is cross section 19-19 of FIG. 19.

FIG. 21 illustrates embedded conductor traces in a biocompatibleinsulative layer in accordance with an embodiment.

FIG. 22 is cross section 22-22 of FIG. 21.

FIG. 23 illustrates a ribbon of embedded traces in accordance with anembodiment.

FIG. 24 is cross section 24-24 of FIG. 23.

FIG. 25 illustrates stacked traces in accordance with an embodiment.

FIG. 26 is cross section 26-26 of FIG. 25.

FIG. 27 illustrates folding up a U-section of a ribbon in accordancewith an embodiment.

FIG. 28 illustrates folding a U-section of a ribbon in accordance withan embodiment.

FIG. 29 illustrates an eye implant power and data transfer architecturein accordance with an embodiment.

FIG. 30 illustrates modeled circuit values of a three-coil system forefficiency determinations in accordance with an embodiment.

FIG. 31 illustrates a brain implant in accordance with an embodiment.

FIG. 32 illustrates a spinal implant in accordance with an embodiment.

FIG. 33 is a flowchart of a process in accordance with an embodiment.

FIG. 34 is a flowchart of a process in accordance with an embodiment.

Reference to the remaining portions of the specification, including thedrawings and claims, will realize other features and advantages of thepresent invention. Further features and advantages of the presentinvention, as well as the structure and operation of various embodimentsof the present invention, are described in detail below with respect tothe accompanying drawings. In the drawings, like reference numbersindicate identical or functionally similar elements.

DETAILED DESCRIPTION

A three-coil power transmission system for implanted devices offers manytechnical benefits. The third, buffer coil increases efficiency of powertransmission between the transmitter coil and receiver coil. It alsoallows another set of design parameters with which to work so that areceiver coil (or transmitter coil) may be sized for small, constrainedspaces. A three-coil structure can tolerate larger misalignments in theX-Y plane between coils than a two-coil structure. This can be importantfor cases in which the receiver coil is buried in the body and notvisible, so an exact determination of its location is unknown. It canalso help mitigate voluntary or involuntary movements of a subject,keeping efficiency high. Further, a three-coil structure can toleratelarger angular misalignments between coils than a two-coil structure.The coils do not need to be aligned as much. This may be especiallyimportant with blind people who cannot fixate their eyes in a certainposition while using retinal implant equipment.

A three-coil system can help in many types of implants, such asintraocular, cortical, and spinal implants. It can be used for imaging,displays, cameras, drug delivery devices, pressure transducers, andother uses that depend on electrical power. Wherever there is a need forefficient wireless power transmission into the body, a third coil mayhelp.

Four, five, six, and greater numbers of coils can be used to furtherincrease efficiency or give more design space so that receiver coils ortransmission coils can be redesigned. Multiple coils may be especiallyuseful when the receiver coil is buried deep within the body, far awayfrom the surface.

A coil for electromagnetic induction fabricated using micromachiningprocesses combined with folding offers many technical benefits. Suchcoils can be manufactured to be extremely small, suitable for highfrequencies. Further, resilient coils can be pinched, flexed, and/orfolded to fit through snug places and then expand back into shape.Electrical conductor traces can be appropriately sized to have a highsurface area-to-volume ratio, minimizing areas of conductor that wouldnot be used because of the skin effect. The skin effect is a descriptionof non-uniform current distribution in a cross section of a conductor athigh frequencies. The higher the frequency, the more that the currentonly flows through the outermost portions (i.e., the skin) of aconductor. Micromachined coils can also be formed to minimize theproximity effect of current at high frequencies. The proximity effect isalso a description of non-uniform current distribution in a crosssection of nearby conductors at high frequencies. The higher thefrequency, the more the current in parallel wires stays away from theopposing wires when the currents travel in the same direction (or staysclose to the other wire when the currents travel in oppositedirections). A quality factor (Q) for a power coil is defined byQ=ωL/Rac, where ω is frequency in radians, L is inductance of the coil,and Rac is resistance to alternating current. Therefore, the lower theRac, the higher the Q. Another benefit is that biocompatible coils canbe micro-manufactured using readily available biocompatible materials.

A U-shaped section of electrical conductor traces that is later foldedto straighten it out offers many technical benefits. A smaller wafer canbe used as a substrate for depositing the traces. For example, a 10centimeter (4 inch) diameter wafer can produce a length of conductorsthat is 20 centimeters (8 inches) long. For a coil that is 1 centimeter(cm) in diameter, a 20-cm long length allows it to be coiled six timesaround, as opposed to only three times around for a 10-cm long length.

Other advantages of these and other aspects will be apparent from thespecification and drawings. Many of the embodiments are explained withrespect to an eye implant; however, other implant uses will be apparent.

It has been found that the lens capsule in an eye is an ideal positionto place an intraocular receiver coil. The lens capsule is just largeenough for a coil, it is within the sclera, and surgical implantationprocedures are well established. After the natural lens is removed, anintraocular coil can be implanted into the lens capsule bag.

Associated with that implant position, two intrinsic challenges forachieving a high-Q coil are the size and equivalent mass. The size of acoil is preferably less than or equal to 10 mm in outer diameter. Adiameter of 9 to 10 mm is generally the maximum, with 9 5 mm being theaverage maximum. The equivalent mass of a coil is preferably equal to orless than 46 milligrams (mg) in saline.

An “equivalent mass” of an item in a liquid is its mass minus the massof liquid displaced by the volume of item. This accounts for bouyantforces on the item.

A buffer coil can be implanted around the cornea and under theconjunctiva of the eye. A buffer coil with a 20 mm diameter has beenfound to be large enough to circumscribe a cornea of an adult human eye,and keep away from resting on it. A buffer coil comprising a litz wirehaving thirty insulated strands of 48 American wire gauge (AWG) wireconductors has been used experimentally to good effect.

The outer diameter of an adult eyeball is generally 23 to 25 mm, with anaverage of 24 mm. A normal human eye can move horizontally ±30° andvertically ±10°.

A transmitter coil of 42 mm in diameter has been determined to workefficiently with a 10-mm receiver coil in the lens capsule and a 20-mmbuffer coil under the conjunctiva. In this configuration, thetransmitter coil and receiver coil end up being separated axially by 25mm, suitable for mounting on a pair of reading glasses.

A 10 megahertz (MHz) carrier frequency has been found to be acceptabledue to a tradeoff between the tissue's radio frequency (RF) absorptionand the coils Q values. All three coils can be tuned to resonate at theoperating frequency with connection to corresponding capacitors inparallel or in series.

FIG. 1A is a perspective, cutaway illustration of an eyeball with aninductively-powered eye implant apparatus having a lens-mounted receivercoil in accordance with an embodiment. Eye 100 includes sclera 102,choroid 104, retina 106, fovea 108, cornea 110, lens 112, iris 114,vitreous humor 116, and optic nerve 118.

Inductively-powered eye implant apparatus includes array of stimulatingelectrodes 120, which is connected with inner-retina neurons of retina106 near fovea 108. Electrical cable 122 couples array 120 withprocessing circuit 124 in lens 112. Processing circuit 124 iselectrically connected with receiver coil 126, which is surrounded in aninsulative biocompatible layer. Buffer coil 128, also surrounded by aninsulative biocompatible layer, is disposed outside sclera 102 andsurrounds cornea 110. In operation during power transfer, buffer coil128 and receiver coil 126 are electromagnetically coupled. Note that nocable piercing the sclera is required for power transfer to thisintraocular device.

Buffer coil 128 receives a varying magnetic field by way ofelectromagnetic induction, and that causes current within buffer coil128 to flow around its ring-like structure. The induced current inbuffer coil 128 causes electromagnetic induction to receiver coil 126,which causes current to be induced in receiver coil 126. The current inreceiver coil 126 flows to processing circuit 124, which rectifies thealternating current (AC) to direct current (DC). The resulting DCvoltage and current is used for powering processing circuit 124 andelectrode array 120.

FIG. 1B is a vertical cross section of the apparatus of FIG. 1A in vivoin which the buffer coil 128 is mounted around cornea 110 and under theconjunctiva 111 of the eye. Besides the structure of the eye enumeratedearlier, other portions are shown. Episclera 101 is the outermost layerof the sclera. As seen in the bottom of the figure, skin 109 gives wayto eyelid 115. Aqueous humor 113 sits within cornea 110. Ciliary body117 holds lens 112 in place.

A cross section of transmitter coil 130 is shown with the direction ofcurrent flow depicted by an X (i.e., into the page) and a dot (i.e., outof the page). The current in transmitter coil 130 induced current in thesame direction in buffer coil 128, which in turn induces current inreceiver coil 126.

Receiver coil 126 is bouyantly supported by sealed, ring-shaped cavity123. Air, nitrogen, an inert gas, or liquid with a specific gravity lessthan an aqueous solution is trapped within sealed cavity 123, loweringthe equivalent mass of the combined receiver coil-sealed cavitystructure. This can be important when using heavier metals for thereceiver coil's traces, such as gold.

FIG. 1C is a vertical cross section of the apparatus of FIG. 1A in vivoin which buffer coil 130 is encapsulated in sclera lens 121. Sclera lens121 is worn by the user, kept tight by suction and meniscus forces onthe eye, bearing on sclera 102. Sclera lens can be applied and removedby a patient as needed for powering the intraocular device or whenefficiency is an issue. Different buffer coils can be easily tested, asno surgical procedure is necessary for the replacement of sclera lenses.

FIG. 1D is a vertical cross section of the apparatus of FIG. 1A withoutthe eye shown for clarity of the dimensions. Transmitter coil 130,buffer coil 128, and receiver coil 126 are shown to scale. Dimensions170-180 that have been found to work for efficient power transmission at10 MHz are shown in Table 1.

TABLE 1 Reference Number in FIG. 1D Description Length 170 outerdiameter of transmitter coil 44 mm 171 inner diameter of transmittercoil 40 mm 172 outer diameter of buffer coil 20 mm 173 inner diameter ofbuffer coil 18 mm 174 outer diameter of receiver coil 10 mm 175 innerdiameter of receiver coil 8 mm 176 axial distance between transmitter 25mm coil and buffer coil 177 axial distance between buffer coil 4.0 mmand receiver coil 178 axial distance between transmitter 25.4 mm coiland receiver coil 179 radial thickness of receiver coil 0.1 mm 180 axialthickness of receiver coil 1.0 mm

FIG. 2 illustrates a wearable transmitter assembly with the transmittercoil in front in accordance with an embodiment. This assembly can beused by patients whose buffer coil is mounted around his or her cornea,either surgically under the conjunctiva or on a sclera lens, and thereceiver coil is within his or her lens capsule.

External unit 200 includes transmitter coil 130 housed in transmitterassembly 232. Transmitter assembly 232 is positioned in front of auser's eye by glasses 234. Other positioning means are envisioned.

Goggles, a helmet with a visor, spectacles, pince-nez, a monocle,binoculars, and/or an externally supported stand can hold thetransmitter coil in front of the user's eyes.

Glasses 234 hold small camera 236 and video processor 238, which areconnected by cable 240 to adaptor 242. Cable 244 connects another portof adaptor 242 to battery pack 246, which can be worn on a belt.

FIG. 3 illustrates a wearable transmitter assembly with the transmittercoil on the side in accordance with an embodiment. This assembly can beused by patients whose buffer coil is affixed to a side of the eyeexternal to the sclera, on the episclera, and their receiver coil ismounted within a vitreous body of the eye within the sclera, to theinside side of the eyeball.

External unit 300 includes transmitter coil 130 housed in transmitterassembly 332. Transmitter assembly 332 is positioned to the side of auser's eye by glasses 334. Other positioning means, such as thosedisclosed above, are envisioned.

Glasses 334 hold small camera 336 and video processor 338, which areconnected by cable 340 to adaptor 342. Cable 344 connects another portof adaptor 342 to battery pack 346, which can be worn on a belt.

A lens capsule is a prime location for mounting a receiver coil. A smallincision may be made if the receiver coil is fashioned so that it issubstantially wider axially than radially and resilient. The receivercoil can then be pinched to transport it through the small incision.

“Substantially wider axially than radially” includes ratios of axialwidth to radial height of 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 15:1,20:1, 25:1, 50:1, 100:1, and other ratios.

FIG. 4A is a picture of pinching and inserting into a lens capsule areceiver coil in accordance with an embodiment. Lens 112 of an porcineeye is surrounded by iris 114. Incision 449 is made in lens 112.Receiver coil 126 has been resiliently pinched to an oblong shape bytweezers 448 and is inserted through incision 449. After receiver coil126 is safely inside the lens capsule, tweezers 448 are drawn back andthe coil is left to regain its shape within lens 112.

FIG. 4B is an annotated picture of the receiver coil of FIG. 4Aspringing to full diameter within the lens capsule. The dotted lineshows an ideal springback shape of receiver coil 126.

FIG. 4C is a picture of the lens capsule of FIG. 4B with the eye's irisremoved for clarity. Note that receiver coil 126 has sprung to a widediameter, filling up the lens capsule. Although it is not perfectlycircular after springing back, it is not necessary for the powertransmitting coil to be perfectly circular. Various shapes can workbecause the system is robust.

To fit inside a lens, it has been found that a circular receiver coilwith an outer diameter equal to or less than 10 mm works well. Theminimum inner diameter of the receiver coil is thought to be equal to orgreater than 6 mm. An axial thickness of equal to or less than 1 mm ispreferred for a 10 mm diameter receiver coil.

From an axial direction, the receiver coil of the exemplary embodimentis circular. However different shapes, including ovals and other roundedshapes, polygons, and hybrid rounded-straight sided shapes areenvisioned. The method of manufacturing described herein allow manyopportunities for geometric shape optimizing.

An “oval” shape includes an ellipse or egg shape. For example, a buffercoil can be oval and have an outer minor axis of about 19 millimetersand an outer major axis of about 24 millimeters. These dimensions havebeen found to be efficient when the major axis is placed horizontallybecause eyes can rotate more horizontally than vertically.

A “polygon” shape includes closed forms with straight edges, including atriangle, quadrilateral, pentagon, hexagon, etc.

FIG. 5 illustrates a receiver coil in accordance with an embodiment.Receiver coil 126 includes conductive pads 554 and 556, which connectall of the traces at each end. Pads 554 and 556 can be electricallyconnected, by soldering or other means, to a processing circuit. Region550 shows a shifting region of the traces that shifts an (axially)internal trace to the outside. This can be helpful in spreading theproximity effect among the traces, thereby lowering the total proximityeffect of the receiver coil.

U-shaped region 552 connects traces wrapping one way around the receivercoil to those wrapping an opposite direction around the coil. Like theregions shown by pad 554, all of the traces may be connected at theU-shaped region end.

FIG. 6 illustrates a receiver coil held by tweezers in accordance withan embodiment. Receiver coil 126 includes conductive pads 654 and 656,which connect all of the traces at each end. U-shaped section 652connects traces wrapping one way around the receiver coil to thosewrapping the opposite direction. Tweezers 648 are shown for scale.

Manufacturing a coil using micromachining techniques on a flat surfacehas its advantages. However, with parallel traces on a two-dimensionalsheet, it is difficult to spread the proximity effect.Microelectromechanical systems (MEMS) technology is used to fashion aMEMS foil coil design with litz wire-like properties. Litz wire-likeproperties are achieved by shifting traces so that when they are foldedand coiled into a ring, the traces trade axial positions in the ring.

FIGS. 7-11 illustrates a ribbon of etched traces on a flat surface withapplicable cross sections in accordance with a method for manufacturinga coil with litz wire-like properties. Ribbon 726 has been manufacturedwith conductive metal traces 766, 768, and seven others. The tracesshift in three discrete areas along the length of the ribbon. Ribbon 726is to be folded along longitudinal fold lines (i.e., creases) 761 and763. Creases 761 and 763, which may or may not be simply lines,longitudinally separate ribbon 726 into three regions or folds: fold760, fold 762, and fold 764.

There are four traces per fold. Trace 766 starts at the upper left offold 760 and snakes down to the opposite (axial, when rolled up) side offold 760 on the right. Meanwhile, trace 768 starts at the secondposition in the upper left of fold 760 and snakes down to cross crease761 and end up in the upper part of fold 762 on the right. Trace 768crosses fold line 761 at a point between cross sections 10-10 and 11-11.

FIGS. 12-14 illustrates folding a ribbon of etched traces to stack themon top of each other in accordance with an embodiment. In FIG. 12,ribbon 726 is flat with folds 760, 762, and 764 in the same plane. InFIG. 13, fold 760 is folded along crease 761 over fold 762. Fold 764 isfolded along crease 763 under fold 762. In FIG. 14, fold 760 and itsembedded conductors are fully stacked on top of fold 762 and itsconductors, which are stacked on top of fold 764 and its conductors. Thefolded ribbon is then wound into a coil.

FIG. 15 illustrates a wound coil of etched traces in accordance with anembodiment. Folded and wound ribbon 726 is shown with each of its threefolds stacked atop one another and then coiled.

FIG. 16 is a cross section of a wound coil of stacked etched traces,along with additional stacks of traces from a U-turn, in accordance withan embodiment. The bottom half of the figure shows folds 760, 762, and764 as they would be stacked when wound into a coil multiple timesaround. Note that the conductor traces shift their axial (i.e.,left-right in the figure) positions. This sharing of the (axial) outsidepositions allows the traces to share the proximity effect, which causesthe current in the traces to flow most freely in the outer positions.

Above the U-turn are folds 1660, 1662, and 1664. These folds started outon the same flat sheet as folds 760, 762, 764, and have been folded overeach other like folds 760, 762, and 764. However, they are folded backto go in an opposite direction over folds 760, 762, and 764. Theresulting stack of folds and U-turned traces is a stack of a total of 24layers. That is, a cross section of the ring has 24 layers. This ismerely one embodiment. Coils with 6, 7, 8, 9, 10, 15, 20, and moretraces per fold are also envisioned as well as coils with more or fewerwrap arounds. The number of stacks is dependent on the number of timesthat the ribbon is coiled upon itself, which itself is dictated by thetarget diameter of the final coil (and length of the flat ribbon).

The U-turn of the conductors is enabled by a U-shaped region in thetraces when they are initially micromachined on a flat surface. ThisU-shaped region, and overall micromachining techniques, are discussedbelow.

FIG. 17 illustrates a flat sheet on a substrate in accordance with anembodiment. Silicon wafer substrate 1770 supports biocompatibleelectrical insulator 1772. Cross section 18-18 is shown in FIG. 18.Biocompatible layer/insulator can include material selected from thegroup consisting of implantable epoxy, liquid crystal polymer (LCP),parylene C, silicone, and other biocompatible materials.

FIG. 19 illustrates etched conductor traces in accordance with anembodiment. Conductor traces 1974 have been applied atop electricalinsulator 1772. Cross section 20-20 is shown in FIG. 20. Conductortraces are manufactured by depositing a thin metal layer on top ofelectrical insulator 1772 and etching away the spaces between thetraces. Other micromachine methods are contemplated. Note that there arethree conductors on each side.

FIG. 21 illustrates embedded conductor traces in accordance with anembodiment. More electrical insulator 2177 has been deposited overconductor traces 1974 to embed them within electrical insulator 2177,forming a biocompatible layer over the conductors.

To “embed” electrical traces in an insulator includes covering them withinsulator sufficient to prevent short circuits at nominal voltages, orotherwise known in the art.

Creases 2176 have been pre-formed in the material by etching awayelectrical insulator in longitudinal lengths. FIG. 22 shows crosssection 22-22.

U-shaped section 2152 connects both sides of conductors to each other.In the exemplary embodiment, it is formed so that all conductor tracesare connected. The lengths of conductor that project from it do so in acommon direction (i.e., up in the figure).

FIG. 23 illustrates a ribbon of embedded traces in accordance with anembodiment. Ribbon 2378 has been created by peeling electrical insulator2177, with its embedded conductor traces 1974, from the flat substrate.

FIG. 24 shows cross section 24-24. Longitudinal depressions have beencreated by further etching in order to facilitate longitudinal foldingalong the creases. Fold 2460 is folded over middle fold 2462, and fold2464 is folded under fold 2462. This stacks the traces in three layers.

FIG. 25 illustrates stacked traces in accordance with an embodiment.This is a result of the folding. FIG. 26 shows cross section 26-26.Folds 2460, 2462, and 2464 are stacked atop one another. This embodimentshows single conductors on each fold for simplicty in illustration.Other numbers of conductors on each layer are envisioned, such as thoseshown in FIG. 14, etc.

FIG. 27 illustrates folding up a U-section of a ribbon in accordancewith an embodiment. Ribbon 2378 is folded such that U-section 2152 isperpendicular to the rest of the ribbon.

FIG. 28 illustrates folding U-section 2152 of ribbon 2378 in half suchthat the lengths of conductor that once projected in the same direction(i.e., up in FIG. 27) now project in opposite directions from oneanother. The result is an extra long ribbon of conductors.

In some embodiments, the U-section does not connect all of the conductortraces to one another but keeps them separately attached to respectiveconductor traces on the other side of the U-section.

FIG. 29 illustrates an eye implant power and data transfer architecturein accordance with an embodiment. Power transmitter 2946 energizestransmitter coil 2930, which electromagnetically couples with buffercoil 2928. Buffer coil 2928 electromagnetically couples with receivercoil 2926 in intraocular system 2924.

Within intraocular system 2924, output from receiver coil 2926 isconnected with rectifier 2981, which rectifies the induced, sinusoidalAC current. The rectified current is sent to reference voltage module2983 and low-dropout regulator 2984. Low-dropout regulator 2984 supplies+1.2 volts (V) to a receiver front end. Rectified current is also sentto SC step-up converter 2982, which supplies low-dropout regulator 2985with power. Low-dropout regulator 2985 supplies +2.4 V, −1.2 V, and −2.4V predominately to a neuro-stimulator array. The neuro-stimulator arrayis intimately connected to electrode array 2920, which is connected withinner-retina neurons of the eye.

FIG. 30 illustrates modeled circuit values of a three-coil system forefficiency determinations in accordance with an embodiment.

Transmitter 3030 is modeled with voltage supply V1, a resistor Rs of 50Ω (ohms) in series with a capacitor Cs of 37.6 picofarads (pF). They areconnected in parallel with grounded resistor Rc of 10Ω with capacitor C1of 177 pF and a coil, modeled with resistor R1 of 0.75Ω and an inductorL1 of 1167 nH (nano Henries).

Buffer coil 3028 is modeled with grounded capacitor C2 of 322 pFconnected in series to a coil, modeled as resistor R2 of 0.54Ω and aninductor L2 of 790 nH.

Receiver 3026 is modeled with a grounded coil, R3 of 1.3Ω and aninductor L3 of 480 nH. They are connected to grounded capacitor C3 of470 pF, then to the anode of Schottky diode D1 (MBR0520L). The cathodeof Schottky diode D1 is connected with grounded capacitor Cr of 30 nFand grounded resistor Rdc of 140Ω.

Using this model, with equivalent loads of 1.9 V and a power consumptionof 25.8 mW, efficiency of the 3-coil system was calculated at 35.9%.This is in comparison to a 2-coil efficiency of 0.7%.

As the eyeball and thus buffer coil and receiver coil are rotated from0° to 30°, efficiencies falls off from 35.9% at 0° to the high teenpercentages at 30°. Thus, even at the maximum angle that an eye canrotate, efficiency is better than in an equivalent 2-coil system.

FIG. 31 illustrates a brain implant in accordance with an embodiment.Deep brain stimulation (DBS) requires an implant to be deeply buriedwithin the brain. This is a candidate for the three-coil system. A100-channel Utah electrode array is connected with a signal processingapplication-specific integrated circuit (ASIC), which can receive powerthrough a thin-film fabricated gold-on-polyimide power coil.

By putting the transmitter coil close to the outer skin of the head anda receiving coil deep inside the skull, efficiency can be improved byintroducing a buffer coil.

In system 3100, buffer coil 3128 is implanted just inside the skullcavity while receiver coil 3126 is deep within the brain. Receiver coil3126 is connected by cable 3122 to electrode 3120. When a transmittercoil inductively couples with buffer coil 3128, efficiency is improvedin transferring energy to receiver coil 3126.

FIG. 32 illustrates a spinal implant in accordance with an embodiment.In system 3200, electrodes 3220 are connected with receiver coil 3226.Buffer coil 3228 allows a more efficient transfer of power from anexternal transmitting coil to receiver coil 3226.

FIG. 33 is a flowchart of a process in accordance with an embodiment.Process 3300 has several operations. In operation 3301, a varyingmagnetic field is generated using a transmitter coil. In operation 3302,the varying magnetic field is received, into a buffer coil affixedexternal to a sclera of an eye, by way of a first electromagneticinduction, the varying magnetic field causing current in the buffercoil. In operation 3303, current is induced, within a receiver coilwithin the eye, by way of a second electromagnetic induction from thecurrent in the buffer coil to the receiver coil. In operation 3304, anintraocular electronic device is powered using the induced current fromthe receiver coil. In operation 3305, the induced current from thereceiver coil is optionally rectified to generate direct current.

FIG. 34 is a flowchart of a process in accordance with an embodiment.Process 3400 has several operations. In operation 3401, conductor tracesare etched on a substrate, the conductor traces underlaid by a sheet offlexible, biocompatible electrical insulator. In operation 3402, moreelectrical insulator is deposited over the conductor traces to embed theconductor traces in the electrical insulator, where the conductor traceson the sheet include a U-shaped region connecting two lengths ofconductor traces that project in a same direction from the U-shapedregion. In operation 3403, the insulator embedded conductor traces arepeeled from the substrate to release a flexible ribbon of the embeddedconductor traces. In operation 3404, the ribbon is folded such that theU-shaped region is perpendicular to the rest of the ribbon. In operation3405, the U-shaped region is folded such that the lengths of conductortraces project in opposite directions from the U-shaped region. Inoperation 3406, the ribbon is round in a spiral to form a closed shape,thereby forming a coil of stacked conductor traces. In operation 3407,leads or pads of the conductor traces are connected to a processingcircuit. In operation 3408, the processing circuit is connected to anarray of stimulating electrodes adapted to be connected withinner-retina neurons in an eye. In operation 3409, an electrical cableis coupled between the coil and the array.

The invention has been described with reference to various specific andillustrative embodiments. However, it should be understood that manyvariations and modifications may be made while remaining within thespirit and scope of the following claims.

1. An inductively-powered eye implant apparatus comprising: a buffercoil adapted to be affixed external to a sclera of an eye, the buffercoil having a conductor covered by a biocompatible layer; a receivercoil adapted for implantation within the eye, the receiver coil having aconductor covered by a biocompatible layer, the receiver coil adaptedfor receiving electrical power by electromagnetic induction through thebuffer coil from a transmitter coil, the buffer coil and receiving coiladapted to be electromagnetically coupled when affixed external to andimplanted within the eye, respectively; and a processing circuitconnected with the conductor of the receiver coil and configured toreceive electrical power from the receiver coil.
 2. (canceled)
 3. Theapparatus of claim 1 wherein the buffer coil is suitable for mountingaround the cornea and under the conjunctiva of the eye.
 4. The apparatusof claim 1 further comprising: a sclera lens encasing the buffer coil,the sclera lens adapted to be worn on the sclera to thereby affix thebuffer coil external to the sclera of the eye.
 5. (canceled)
 6. Theapparatus of claim 1 wherein the buffer coil is oval and has an outerminor axis of about 19 millimeters and an outer major axis of about 24millimeters, the buffer coil adapted to be affixed external to thesclera such that the outer major axis is substantially horizontal. 7.(canceled)
 8. The apparatus of claim 1 wherein the receiver coil issuitable for implantation within a lens capsule of the eye. 9-10.(canceled)
 11. The apparatus of claim 1 further comprising: a sealedcavity attached to the receiver coil; and a fluid disposed within thesealed cavity, the fluid having a specific gravity less than aqueoussolution, thereby adding buoyancy to the receiver coil. 12-13.(canceled)
 14. The apparatus of claim 1 wherein: the buffer coil isadapted to be affixed to a side of the eye external to the sclera; andthe receiver coil is adapted for mounting within a vitreous body of theeye inside the sclera to an internal side of the eye.
 15. The apparatusof claim 1 wherein the receiver coil has a cross section that issubstantially wider axially than radially, allowing the receiver coil tobe resiliently pinched to fit through an incision.
 16. The apparatus ofclaim 1 wherein the receiver coil comprises etched conductors within afolded ribbon of electrical insulator.
 17. The apparatus of claim 1wherein the receiver coil was produced by: etching conductor traces onan electrically insulative sheet; depositing electrical insulator overthe etched conductor traces sufficient to embed the etched conductortraces; folding the sheet over onto itself, stacking the embeddedconductor traces; and then winding the folded sheet in a spiral to forma closed shape.
 18. The apparatus of claim 17 wherein each stackedconductor trace travels across at least one longitudinal fold creasesuch that respective conductor trace discretely shifts radial positionin the spiral at each fold crease crossing.
 19. The apparatus of claim18 wherein each stacked conductor trace progresses parallel with atleast one other stacked conductor trace before traveling across the atleast one longitudinal fold crease to be radially separated from the atleast one other stacked conductor trace.
 20. (canceled)
 21. Theapparatus of claim 17 wherein the conductor traces on the electricallyinsulative sheet include a U-shaped region connecting two lengths ofconductor traces that project in a same direction from the U-shapedregion, the production of the receiver coil further produced by: foldingthe sheet, before the winding, such that the U-shaped region isperpendicular to the sheet; and then folding the U-shaped region suchthat the lengths of conductor traces project in opposite directions fromthe U-shaped region. 22-31. (canceled)
 32. The apparatus of claim 1wherein the buffer coil is affixed to the eye or the receiving coil isimplanted within the eye.
 33. A method of efficiently receiving powerinside an eye for an intraocular electronic device without ansclera-piercing cable, the method comprising: receiving, into a buffercoil affixed external to a sclera of an eye, a varying magnetic field byway of a first electromagnetic induction, the varying magnetic fieldcausing current in the buffer coil; inducing current, within a receivercoil within the eye, by way of a second electromagnetic induction fromthe current in the buffer coil to the receiver coil; and powering anintraocular electronic device using the induced current from thereceiver coil.
 34. The method of claim 33 further comprising: rectifyingthe induced current from the receiver coil to generate direct current.35-50. (canceled)
 51. An inductively-powered implant apparatuscomprising: a buffer coil adapted to be affixed within a portion of abody of a patient, the buffer coil having a conductor covered by abiocompatible layer; a receiver coil adapted for implantation within adeeper portion of the body than the buffer coil, the receiver coilhaving a conductor covered by a biocompatible layer, the receiver coiladapted for receiving electrical power by electromagnetic inductionthrough the buffer coil from a transmitter coil, the buffer coil andreceiving coil adapted to be electromagnetically coupled; and aprocessing circuit connected with the conductor of the receiver coil andconfigured to receive electrical power from the receiver coil.
 52. Theapparatus of claim 51 wherein the portion of the body includes a head,and the processing circuit includes a brain pacemaker.
 53. The apparatusof claim 51 wherein the portion of the body includes a torso, and theprocessing circuit includes a spinal cord stimulator.
 54. The apparatusof claim 51 further comprising: a rechargeable battery configured toreceive electrical power through and be recharged by the processingcircuit.